The invention concerns a measuring head holder for a measuring head, for example but not exclusively an optical measuring head.
A typical form of optical measuring head is for example a 3-D speckle interferometry measuring head by means of which deformation and/or the contour of a surface of an object can be measured by a non-destructive procedure. For that purpose, the measuring head has to be moved into a defined position relative to the surface of the object whose surface is to be measured, and has to be held in that properly defined position during the measurement procedure.
In that respect a problem which frequently arises is that a measuring head can measure and survey on the object a measurement area which may be some square centimeters in size, whereas the object whose surface is to be measured is substantially larger. In such situations, there is frequently a wish to measure the surface of the object at a plurality of measurement locations thereon, in particular when the object is in different conditions and states. It is then necessary to measure the various measurement locations on the object firstly in an initial condition or state of the object and then for example in a condition or state of the object in which it is subjected to a loading.
As such a measuring head is generally a highly expensive component, the procedure adopted usually involves employing one and the same measuring head in succession at each of the individual measurement locations on the object whose surface is to be measured, rather than using a plurality of different measuring heads. It will be appreciated that it is important to achieve in that respect reproducible results in the respective conditions or states of the object whose surface is to be measured.
An object of the present invention is to provide a measuring head holder affording a simple and inexpensive way of holding a measuring head in a uniform position relative to an object whose surface is to be measured during measurement procedures.
Another object of the present invention is to provide a measuring head holder which can be previously secured to an object whose surface is to be measured in a properly defined position in order thereby to prepare the object for the measuring procedure, so that the measuring head can then be fixed to the fitted measuring head holder in a defined position and released therefrom again after measurement.
Still a further object of the present invention is to provide a measuring head holder for carrying a measuring head for measuring a surface of an object, for example using a 3-D speckle interferometry technique, which is of a simple design configuration and structure while nonetheless ensuring mounting of a measuring head thereto in the appropriately defined position.
In accordance with the principles of the present invention the foregoing and other objects are attained by a measuring head holder for mounting a measuring head, for example for implementing a 3-D speckle interferometry procedure on an object to be measured, wherein the measuring head holder has a mounting or receiving portion for definedly securing thereto a measuring head, and at least one securing element for fixing the mounting or receiving portion to said object.
As will be seen in greater detail from the description hereinafter of preferred embodiments of the invention, the fact that the measuring head holder includes a mounting or receiving portion, which can be referred to hereinafter for the sake of brevity just as the receiving portion, means that the measuring head can be released from the measuring head holder at any time without the holder being removed from the object to which it is mounted.
The fact that the receiving portion includes at least one securing element also means that the receiving portion can be fixed to the object, independently of the fixing of the measuring head to the holder.
In a preferred feature of the invention the receiving portion can be in the form of a mounting or adaptor ring having a central through opening, the longitudinal direction of which coincides with the observation direction of the measuring head. That arrangement ensures very stable securing of the measuring head to the object as the ring shape of the receiving portion guarantees a high level of stability without observation of the object whose surface is to be measured by the measuring head being adversely affected.
The measuring head holder may include as securing elements feet or legs, referred to hereinafter for convenience as feet, which are secured on the one hand to the receiving portion, more especially when in the form of an adaptor ring, and which on the other hand bear with their respective free front ends against the surface of the object. That arrangement provides that it is possible on the one hand to suitably select the number of mounting or attachment points, in general three such points to provide a properly defined but not over-defined mounting or support configuration. On the other hand, the position of the feet can be suitably selected in accordance with the shape of the object insofar as the holder or adaptor ring can have a plurality of possible mounting positions for the feet thereon.
To provide for maximum stability in terms of positioning of the measuring head holder with respect to the object whose surface is to be measured by the measuring head, the mounting points of the feet could be spaced away from each other to the maximum extent achievable in regard to the structure of the holder, that is to say for example the feet can extend inclinedly outwardly from the adaptor ring. That however gives rise to the problem that on the one hand association of the measuring area to be observed by the measuring head, in regard to position on the surface of the object, is something that can only be achieved with difficulty, while on the other hand there is also the problem that, in the event of deformation of the surface of the object in the measuring area being measured by the measuring head, it is not clear how the surface of the object is displaced with respect to the measuring area. With those considerations in mind, the mounting points of the measuring head holder and more particularly the mounting points of the feet on the surface of the object, will desirably be so selected that at least one of the mounting points and preferably in particular all mounting points are close to or precisely just in the measuring area.
In addition, the contact points of the measuring head holder and in particular the contact points of the feet are such that either only one mounting point, that is to say a foot, always remains fixedly on its point on the object, whereas the other two out of three can move along the surface of the object or, instead of the other feet, there can be an independent holding means which is external with respect to the object to be measured, for example a robot arm.
An alternative in this respect provides that all contact points of the feet against the object are arranged fixedly on the object and for example upon extension or elongation of the surface of the object, the feet experience elastic deformation which is uniform in regard to all feet.
While in the former case the fixed mounting point serves as a fixed point between the measuring area and the surface of the object even when the surface of the object experiences deformation, in the second case the fixed point between the surface of the object and the measuring area is the geometrical center between the fixed mounting points, thus generally the geometrical center of the above-mentioned adaptor ring which can preferably form the receiving portion.
A further possible structural configuration provides that there are at least three feet or legs on the adaptor ring, which ensure that there is a spacing that is always the same between the adaptor ring and the surface of the object, that is to say the length of the legs remain the same, without one of the mounting points serving as a fixed point. This is also sufficient to resolve the problem which arises from a mathematical point of view, of a system of equations comprising three equations with three unknowns. It will be appreciated however that in this respect the displacement of the measuring area may not be so great, between the initial condition and the measurement condition, that there are no longer any overlaps of the measuring areas in the two conditions or states.
The adaptor ring is preferably secured to the object in particular independently of the measuring head, using any suitable means, more particularly for example by means of spring force, elastic biasing of levers, vacuum suction devices, and more especially by means of mechanisms using levers which are movable into a locking condition by passing over a dead center point, that is to say with an over-center locking action, or by means of magnetic force. For that purpose, in a particular embodiment clamping pins or bolts can be screwed in laterally outwardly projecting relationship into the above-mentioned adaptor ring. Magnetic holders which are to be held to the magnetic surface of the object to be measured can then be suitably secured to the clamping pins or bolts. The magnetic holders are preferably elastically variable in terms of their configuration between the holders which fit to the surface of the object and the clamping pins or bolts, for example by means of suitable springs incorporated therebetween. Alternatively, the clamping pins or bolts can be used to secure clamping belts, straps, cords or like elements which extend around or embrace the object, to hold the measuring head holder to the surface of the object.
The measuring head is secured to the measuring head holder, for example to the above-mentioned adaptor ring, in a defined fashion such that it can be released at any time, by way of suitable fitting elements on the one hand and fixing means such as for example screw means on the other hand. The fitting elements such as fitting bores or pins fitted into the fitting bores or for example balls and the like which engage into central bores are arranged in particular on an annular flat rear face of the adaptor ring. Fitting pins which are fixedly arranged at the appropriate side of the measuring head can fit into the fitting bores, or inserted into the fitting bores are fitting pins which also fit into corresponding counterpart bores in the measuring head.
In particular the fitting elements can be arranged in such a way that the measuring head can also be fitted to the adaptor ring only in a given specific position.
In that case fixing can be effected for example by way of screw means between the measuring head and the adaptor or mounting ring. For that purpose, arranged on the ring are through openings which extend in the longitudinal direction, more particularly being distributed over the periphery thereof at a plurality of spaced locations.
In operation of the assembly, when the surface of an object is irradiated with laser light and in particular when using a superimposed reference beam technique, the contour of the surface of the object may be relatively difficult to detect. Therefore, white light illumination or illumination with visible light can make it easier to associate the measurement result with the surface of the object. For that purpose the measuring head holder and for example the measuring head also may include a light source emitting visible light, for example a white light emitting diode directed on to the object whose surface is to be measured.
So that tensile loadings which occur at the cable which supplies the measuring head do not have an effect on the contact between the measuring head holder and the object to which it is mounted, the arrangement may include in particular a means for relieving tensile loading on the cable, in the form of an elastic resilient cable loop as a means for buffering variations in length of the cable. This can be implemented in the form of a rubber sleeve which is resilient in the longitudinal direction, in the form of a loop or curl in the cable by means of a resilient loop-forming assembly, or by simply forming the cable in a helical or spiral configuration.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of preferred embodiments.